When Sarah and Felix examine the information about the prisoner they are hunting, Malone, the information they receive indicates he was imprisoned for 'aggravated homicide.' In England and Wales, the correct term is murder. By 1978, when Malone was supposed to be imprisoned, the offense would be stated as 'murder,' with specific aggravating and mitigating factors taken into account in sentencing. The previous offense of aggravated murder, under the Homicide Act 1957, was abolished in 1965.
When Sarah and Felix meet with Kassov, he states he got the information about the prisoner from 'a friend in the parole service.' In England and Wales, parole is supervised by the Probation Service.
In the very last scene where Siobhan is pointing a weapon at her mother, you can clearly see a security pin inside the guns barrel revealing that it is only a prop.
The "Bayonet Public House" where Mrs. S, Felix and Sarah meet Terrence has a Union Flag and an Irish Republican Flag hanging on the wall, which is most unlikely.
Terrence is throttled with a flex fitted with a north/central American IEC-Type B plug rather than a United Kingdom IEC-type G plug.
When arriving at the pub in London where Mrs. S, Felix and Sarah meet Terrence, their black London taxi and other vehicles drive on the right-hand-side of the road, and other vehicles are shown parked on the wrong side of the road, given that in the UK vehicles drive on the left.